Low back pain (LBP) is a common and costly condition. Most patients with acute LBP enter the healthcare system through primary care providers. Primary care management is currently characterized by a high degree of variation. Unexplained and unwarranted variability has been documented in primary care practice for variety of clinical decisions including referral to specialties such as physical therapy. Given the variations in care, it is not surprising that the outcomes of primary care management are also highly variable. Most patients improve, yet a considerable proportion goes on to recurrence and chronicity. Direct healthcare costs associated with these patients can be substantial, and indirect costs related to lost work productivity are high. Physical therapy management of patients with acute LBP is also highly variable in terms of interventions used and outcomes achieved. Developing more effective management strategies for patients with acute LBP that are feasible for wide-spread clinical adoption presents an opportunity to standardize and improve care for a very common and expensive condition. Current clinical practice guidelines for primary care management of patients with acute LBP recommend a stepped care approach, involving initial management of advice and reassurance, with referral to specialists such as physical therapy used only after several weeks for patient who fail to recover. Recent research has developed a decision rule identifying a sub-group of patients with LBP likely to experience rapid, sustained improvement with a specific physical therapy intervention, suggesting it may be more cost-effective to consistently manage this sub-group with referral for this specific treatment. The impact of standardizing primary care and physical therapy management using this decision rule has not been assessed. The proposed study seeks to compare the effectiveness of the usual, stepped care approach to the alternative approach of early implementation of physical therapy for this group of patients with acute LBP. Specific aims are to compare the clinical effectiveness, costs (direct and indirect), and cost-effectiveness of the two different management approaches. This study is a randomized trial examining primary care management of a sub-group of patients with acute LBP. One group will receive care standardized around the decision rule with early implementation of physical therapy. The other will be managed with the usual stepped care approach of delayed referral. Outcomes will include measures of disability, pain, satisfaction, and costs over 1 year. This study will permit an examination of the effectiveness and costs associated with two different approaches to primary care management of a group of patients with acute LBP. The results of this study will help to determine the most effective management strategies about which care should be standardized.